Dependence on fossil fuel of human being, shocking oil price increase and environmental awareness have driven strong development and deployment of electric vehicles (EVs). EVs' batteries can be recharged by connecting to the grid. Recently, to charge such batteries, the most common way is conductive connection between batteries and chargers; the power is transferred by a copper cable connected to the grid. However conductive connection has many drawbacks, such as: (a) risk of electric shock to users, (b) fire hazards, (c) short-circuit and (d) inconvenience for users.
Contrary to traditional conductive charging, wireless charging is safe, convenient and autonomous for electric vehicles. Wireless charger is safe for users as it is innately isolated from the grid. It transfers power via a large gap from transmitting coils to receiving coils mounted on the vehicle. Wireless charging can be done without any inconvenience caused by bundle of cables, connectors and plugs. Therefore it becomes an autonomous charging system.
Current wireless power technique can be classified into two types: (1) magnetic resonance and (2) inductive transfer. Magnetic resonance using radio wave often operates at frequencies of hundreds of MHz to GHz level. This allows the application of this method at greater distances. However this technique can be mainly used in signal transmission; it is almost impossible to apply this technique in power applications. Magnetic resonance using frequency range of around a few Mhz usually has low coupling factors (below 0.1). Beside that magnetic resonance charging operate at this frequency level intensifies electromagnet compatibility (EMC) problems and also makes it challenging for power electronic converters used with the chargers.
Conventional inductive transfer has been utilized in home appliances and electronic gadgets such as electric shavers, mobile phones, cameras; however operating range of these applications limits within some centimeters range. Inductive power transfer using near-field magnetic resonance phenomenon is relatively novel technique. This technique uses an intermediate range of frequency and it is attractive for power applications, such as wireless power chargers for battery system in electric vehicles, as it can transmit high power effectively at the range of several decimeters to meters. For such inductive transfer system, the resonant frequency can be properly tuned by connecting with an external capacitor. Nevertheless in such system, the voltage in the sending coil and the capacitor can easily reach thousands of volts at the resonant frequency. This high voltage prevents an implementation of a practical inductive power transfer, especially for high power applications.
This section provides background information related to the present disclosure which is not necessarily prior art.